The overall goal of this project is to elucidate the role of coagulation proteins in platelet function. Current work is aimed at studies of interaction between platelets and thrombin. Work in progress suggests that platelets contain a storage pool of microtubular protein in dense granules. Thrombin can produce a mobilization of the stored microtubular protein to form new microtubules upon platelet activation. This unique aspect of platelet-thrombin interaction may play a functional role in irreversible platelet activation and the release of platelet lysosomal enzymes. Further investigation will be aimed at developing a procedure to isolate and purify plasma membrane from thrombin-treated platelets followed by chemical characterization of these membranes. The proposed work is also intended to study the functional role of platelet fibrinogen in thrombin-induced aggregation.